Diseño de columnas css liquid

[marweb]

no me funciona se pierde la columna en firefox, lo testee en ie e igual te pongo el codigo:

Código:

<div id="maincontainer">
<div id="topsection"><div class="innertube"><h1>CSS Liquid Layout #3.1- (Fixed-Fluid-Fixed)</h1></div></div>
<div id="contentwrapper">
<div id="contentcolumn">
<div class="innertube"><b>Content Column: <em>Fluid</em></b> <script type="text/javascript">filltext(45)</script></div>
</div>
</div>
<div id="leftcolumn">
<div class="innertube"><b>Left Column: <em>230px</em></b> <script type="text/javascript">filltext(20)</script></div>
</div>
<div id="rightcolumn">
<div class="innertube"><b>Right Column: <em>200px</em></b> <script type="text/javascript">filltext(15)</script></div>
</div>
<div id="footer"><a href="http://www.dynamicdrive.com/style/">Dynamic Drive CSS Library</a></div>
</div>

y este es el css

Código:

/* CSS Document */
body{
margin:0;
padding:0;
line-height: 1.5em;
}

b{font-size: 110%;}
em{color: red;}

#topsection{
height: 110px; /*Height of top section*/
}

#topsection h1{
margin: 0;
padding-top: 15px;
}

#contentwrapper{
float: left;
width: 100%;
}

#contentcolumn{
margin: 0 200px 0 230px; /*Margins for content column. Should be "0 RightColumnWidth 0 LeftColumnWidth*/
}

#leftcolumn{
float: left;
width: 230px; /*Width of left column*/
margin-left: -100%;
}

#rightcolumn{
float: left;
width: 200px; /*Width of right column*/
margin-left: -200px; /*Set left marginto -(RightColumnWidth)*/
}

#footer{
clear: left;
width: 100%;
background: black;
color: #FFF;
text-align: center;
padding: 4px 0;
}

#footer a{
color: #FFFF80;
}

.innertube{
margin: 10px; /*Margins for inner DIV inside each column (to provide padding)*/
margin-top: 0;
}